Method and apparatus for forming an HSG-Si layer on a wafer

ABSTRACT

An HSG-Si layer is formed on a wafer under a uniform temperature condition. An apparatus for forming the HSG-Si layer includes a housing forming a process chamber, a first heater on which the wafer is positioned fixed in place at the bottom of the process chamber, a second heater at the top of the process chamber, and a thermal insulator which prevents the heat generated by the first heater from being transferred to the outside of the process chamber. A temperature control system regulates the temperature of the heaters. A method of forming the HSG layer includes steps of placing the wafer on the first heater, using the heaters to remove moisture from the wafer, injecting a source gas of the HSG-Si toward the upper surface of the wafer to form amorphous silicon on the wafer, and annealing the wafer for a predetermined period of time to transform the amorphous silicon into an HSG-Si layer. During the steps of forming the HSG-Si layer, the temperatures of the first and second heaters are regulated to maintain the surface temperature of the wafer constant.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to method and apparatus for formingan HSG-Si (hemispherical grained silicon) layer. More particularly, thepresent invention relates to a method and apparatus for forming anHSG-Si layer on a wafer in the manufacturing of semiconductor memorydevices.

[0003] 2. Description of the Related Art

[0004] In general, semiconductor devices are manufactured by coating asilicon wafer with a thin film having predetermined electricalcharacteristics, using a semiconductor manufacturing apparatus. The thinfilm is typically formed on the wafer by executing a series ofsemiconductor processes such as lithography, chemical and physical vapordeposition, plasma etching, HSG-Si manufacturing processes or the like.The wafer coated with the thin film is used for manufacturingsemiconductor devices and chips.

[0005] Among the above-mentioned semiconductor manufacturing processes,the HSG-Si manufacturing process is widely used to increase the surfacearea of a capacitor, thereby increasing the capacitance. HSG-Si iscommonly manufactured by depositing silicon under a predetermineddeposition condition or by depositing amorphous silicon and transformingthe silicon into HSG-Si. These types of HSG-Si manufacturing methods aredisclosed in U.S. Pat. No. 5,885,869 (issued to Charles Turner et al. onMar. 23, 1999) and U.S. Pat. No. 5,759,864 (issued to Homg-Huei Tseng etal. on Jun. 2, 1998).

[0006]FIG. 1 shows a semiconductor processing system 500 for carryingout a conventional HSG-Si manufacturing process. As shown in FIG. 1, theconventional semiconductor processing system 500 includes a processchamber 510. A first heater 520 for heating a wafer 400 is installed inthe process chamber 510. The lower surface of the first heater 520 issupported by a support member 522. The wafer 400 is introduced into theprocess chamber 510 through a guide slot 514 formed on one side of theprocess chamber 410, and is positioned on the first heater 520.

[0007] A thermocouple 525 for detecting the temperature of the firstheater 520 and a current supplying line 523 for supplying a current tothe first heater 520 are provided beneath the first heater 520. Thethermocouple 525 and the current supplying line 523 are connected to acontroller (not shown). The controller supplies the current to the firstheater 520 through the current supplying line 523 based on thetemperature of the first heater 520 detected by the thermocouple 525,thereby maintaining the temperature of the first heater 520 within apredetermined range.

[0008] The wafer 400 is fed into the process chamber 510 by a handler(not shown), and a control section (not shown) operates a valve device516 to open/close the guide slot 514 so that the wafer 400 can be guidedinto the process chamber 510.

[0009] The process chamber 510 includes a dome-shaped roof 512, and asecond heater 521 is installed on an upper portion of the dome-shapedroof 512 in such a manner that it surrounds the dome-shaped roof 512.The radiant heat created in the process chamber 510 by the first andsecond heaters 520 and 521 is directed to the wafer 400 by thedome-shaped roof 512.

[0010] An RF (Radio Frequency) electrode 540 to which an RF current isapplied is installed between the dome-shaped roof 512 and the secondheater 521. When a gas such as silane, disilane, or the like is injectedfrom a gas injector 530, RF electric waves are irradiated into theprocess chamber 510 through the RF electrode 540 to activate the gas.The gas injector 530 is connected to a gas supplying line 538, and thegas is supplied to the gas injector 530 through the gas supplying line538 from a gas source (not shown).

[0011] One side of the process chamber 510 communicates with adischarging port 532. The discharging port 532 is connected to a vacuumpump 535 so that a vacuum can be created in the process chamber 510.

[0012] A wafer holder 560, which receives the wafer 400 guided towardfirst heater 520 and places the wafer 400 on the upper surface of thefirst heater 520, is installed in the process chamber 510. The waferholder 560 includes a first arm portion 562 disposed at a peripheralportion of the upper surface of the first heater 520, a second armportion 564 engaged with a wafer holder driving apparatus 570, and asupport 566 connecting the first arm portion 562 and the second armportion 564. Although only one first arm portion 562, one second armportion 564, and one support 566 are shown in FIG. 1, the wafer holder560 comprises three or more sets of such components.

[0013] The wafer holder driving apparatus 570 comprises a cylinder 572provided below the process chamber 510. A bellows 580 provides a sealbetween the cylinder 572 and the process chamber 510 so that the vacuumstate of the process chamber 510 is maintained.

[0014] A plunger 574 is disposed in the cylinder 572 and is movable inupward and downward directions. A shaft 576 is engaged with the uppersurface of the plunger 574, and the upper end portion of the shaft 576is engaged with the end portion of the second arm portion 564. Ahydraulic pressure supplying section 578 supplies hydraulic pressure tothe cylinder 572 to move the plunger 574 in the cylinder 572.

[0015] In addition, the conventional semiconductor processing system 500includes a heater moving apparatus 600 for moving the first heater 520upward and downward. The heater moving apparatus 600 comprises a motor608 generating a driving force and a lift 610 which is connected to themotor 608 in such a manner that it can move up and down.

[0016] The lift 610 is fixed to the lower surface of a bellows cover620, and moves the bellows cover 620 upward and downward when the motor608 is operated. The bellows cover 620 includes an upper cover 622fixedly attached to the bottom of the process chamber 510 and a lowercover 624 which is moved upward and downward by the lift 610. When thelift 610 is moved upward, the upper cover 622 is maintained in a fixedstate and the lower cover 624 is moved into the upper cover 622.Further, the support member 522 of the first heater 520 is mechanicallyconnected to the lower cover 624 so as to move together with the lowercover 624, so that the first heater 520 can be moved upward and downwardin the process chamber 510.

[0017] Hereinafter, the operation of the of the above-describedconventional semiconductor processing system 500 for manufacturing anHSG-Si will be explained.

[0018] When the HSG-Si manufacturing process starts, the valve device516 opens the guide slot 514 whereupon the wafer 400 is moved into theprocess chamber 510 by the handler.

[0019] When the wafer 400 has been moved into a position over the uppersurface of the first heater 520, the wafer holder 560 is moved-upward bythe wafer holder driving apparatus 570 to receive the wafer 400, andthen is moved downward to position the wafer 400 on the upper surface ofthe first heater 520. At the same time, the controller applies operationsignals to the first and second heaters 520 and 521 so as to operate thefirst and second heaters 520 and 521. At this time, the temperature ofthe first heater 520 is about 700 to 750° C., the temperature of thesecond heater 521 is about 315 to 325° C., and the temperature of thewafer 400 is about 600 to 610° C.

[0020] Then, the controller applies operation signals to the heatermoving apparatus 600 in order to move the first heater 520 upward to afirst position A in the process chamber 510. Placing the first heater520 at the first position A in the process chamber 510 improves theefficiency of heating the wafer 400. At the first position A the firstheater 520 is at a level corresponding to that of the gas injector 530,and is vertically displaced upwardly from its initial position by about80 mm.

[0021] At this time, the temperatures of the first and second heaters520 and 521 are maintained constant, but the temperature of the wafer400 is raised to 615-625° C. due to the heat radiating in the processchamber 510.

[0022] Thereafter, the first heater 520 is left at the first position Afor about one minute. The time period of one minute is required forremoving foreign substances such as moisture from the wafer 400.

[0023] After one minute has passed, a gas is injected on the wafer 400.The gas acts as a source for forming HSG-Si on the wafer 400, and forthis purpose a reactive gas such as silane or disilane or the like isused. Then, the RF current is applied to the RF electrode 540 so thatthe RF electric waves are irradiated into the process chamber 510, toactivate the source gas.

[0024] When the gas injecting process has been completed, the controlleroperates the heater moving apparatus 600 to move the first heater 520upward to a second position B in the process chamber 510. Placing thefirst heater 520 to the second position B in the process chamber 510accelerates the growth rate of the HSG-Si by raising the temperature ofthe wafer 400.

[0025] At the second position B, the first heater 520 is displacedvertically upward from its initial position by about 100 mm. At thistime, the heating temperatures of the first and second heaters 520 and521 remain constant, but the temperature of the wafer 400 is raised to625-635° C. by the heat radiating in the process chamber 510. The gasinjected on the wafer 400 is thermally decomposed when the heater 520 isat the second position B, whereby the HSG-Si layer is formed on thewafer 400.

[0026] After the formation of the HSG-Si layer has been completed, thecontroller operates the heater moving apparatus 600 to return the firstheater 520 to its initial position, and then opens the valve device 516.Then the handler moves into the process chamber 510 and feeds the wafer400 to the next stage of the semiconductor device fabrication equipment.

[0027] However, in the conventional semiconductor processing system 500,the temperature in the process chamber 510 varies as the first heater520 is moved in the process chamber 510 while the HSG-Si process isproceeding. As it is known that HSG-Si forms best under a uniformtemperature condition, the unstable temperature condition occurring dueto the movement of the first heater 520 can produce defects in theHSG-Si layer.

[0028] Furthermore, the heater moving apparatus 600 for moving the firstheater 520 upward and downward renders the overall structure of theapparatus complex, and contributes significantly to the manufacturingcost of the apparatus.

[0029] Furthermore, moving the first heater 520 upward and downwardduring the forming of the HSG-Si layer takes time, thereby detractingfrom the productivity of the manufacturing process.

SUMMARY OF THE INVENTION

[0030] The present invention has been made to solve the above-describedproblems.

[0031] Accordingly, one object of the present invention is to provide amethod of forming an HSG-Si layer in a relatively short amount of timeand under a uniform temperature condition, thereby preventing defectsfrom occurring in the HSG-Si layer and contributing to the overallefficiency and productivity of a semiconductor device manufacturingprocess. Another object of the present invention is to provide anapparatus of a relatively simple structure for forming an HSG-Si layerunder a uniform temperature condition, thereby preventing defects fromoccurring in the HSG-Si layer and reducing equipment costs associatedwith a semiconductor device fabrication facility.

[0032] In order to achieve the first object, the present inventionprovides a method of forming an HSG-Si layer wherein the temperature ofthe ambient in a process chamber is maintained constant by regulatingthe temperature of a first heater fixed in place at the bottom of theprocess chamber and a second heater surrounding the upper portion of theprocess chamber. A wafer having a silicon layer is placed on a centralportion of the first heater and foreign substances are removed from thewafer by using the first and second heaters and the heat radiatingwithin the process chamber. Thereafter, a source gas is injected ontothe silicon layer of the wafer and the wafer is annealed for apredetermined time, while the first heater remains fixed in place andtemperatures of the heaters are regulated to maintain the surfacetemperature of the wafer constant, so that a uniform HSG-Si layer isformed from the silicon layer.

[0033] In order to achieve the second object, the present inventionprovides a semiconductor processing apparatus having a housingconstituting a process chamber in which the HSG-Si manufacturing processis performed, a first heater fixed in place at the bottom of the processchamber, a gas injector disposed at the same level as the first heater,and a thermal insulator which insulates the process chamber to preventthe loss of heat from the process chamber.

[0034] A second heater for raising the temperature in the processchamber may be provided at the top of the process chamber. The upperportion of the housing constituting the process chamber is preferablydome-shaped so that the heat radiating from the first heater is directedtoward the wafer.

[0035] A temperature control system allows the temperature of the firstand second heaters and, hence, the temperature of the ambient within theprocess chamber and the surface temperature of the wafer itself, to beregulated. The temperature control system includes at least onetemperature sensor, such as a thermocouple, and a current supply lineattached to the first heater.

[0036] The gas injector injects a gas onto the upper surface of thewafer positioned on the first heater so that an HSG-Si layer can begrown on a silicon layer of the wafer. An RF electrode may be providedbetween the upper portion of the process chamber and the second heater.RF electric waves are irradiated into the process chamber when the gasis injected toward the upper surface of the wafer, thereby activatingthe gas.

[0037] The insulator preferably includes a quartz member extending overthe inner surface of a wall of the housing at the lower portion of theprocess chamber. The wall has an interior space, which is preferably inthe state of a vacuum to prevent the transfer of heat from the innerwall surface at the bottom of the process chamber to the outer wallsurface at the bottom of the process chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription thereof made with reference to the accompanying drawings, ofwhich:

[0039]FIG. 1 is a schematic diagram of a conventional semiconductorprocessing system used to form an HSG-Si layer on a wafer;

[0040]FIG. 2 is a schematic diagram of a semiconductor processing systemused to form an HSG-Si layer on a wafer according to the presentinvention;

[0041]FIG. 3 is a schematic diagram of a portion of the semiconductorprocessing system comprising a thermocouple and a power supplying lineinstalled on the bottom of a heater;

[0042]FIG. 4 is a cross-sectional view of a wafer fed into a processchamber;

[0043]FIG. 5 is a cross-sectional view of the wafer showing an HSG-Silayer formed on the wafer; and

[0044]FIG. 6 is a flow chart of an HSG-Si manufacturing processaccording to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Hereinafter, a preferred embodiment of the present invention willbe explained in detail with reference to the attached drawings.

[0046] Referring to FIG. 2 an apparatus 100 for forming an HSG-Si layeron a wafer according to the present invention includes a housing 101forming a process chamber 110 therein. The housing 101 includes a bottomwall 117 extending along the bottom of the process chamber 110.

[0047] A first heater 102 for heating a wafer 200 is fixed in place inthe process chamber 110. More specifically, the bottom surface of thefirst heater 102 is supported by a support member 125 fixed to thebottom wall 117 of the housing 101. The wafer 200 is introduced into theprocess chamber 110 through a guide slot 114 formed at one side of theprocess chamber 110 and is positioned on the upper surface of the firstheater 102.

[0048] Referring to FIG. 3, first and second thermocouples 122 and 123for detecting temperatures of the central and peripheral portions of thefirst heater 102 and a current supplying line 124 for supplying acurrent to the first heater 102 are attached to the bottom surface ofthe first heater 102. The first thermocouple 122 is attached to acentral portion of the bottom surface of the first heater 102 andextends downwardly therefrom, and the second thermocouple 123 isattached to the peripheral portion of the bottom surface of the firstheater 102 at one side thereof and extends downwardly therefrom.

[0049] The first and second thermocouples 122 and 123 and currentsupplying line 124 are connected to a controller 300. The controller 300supplies a current to the first heater 102 through the current supplyingline 124 based on the temperature of the first heater 102 detected bythe first and second thermocouples 122 and 123 so that the temperatureof the first heater 102 is maintained within a predetermined range.

[0050] It is preferable that the temperature of the first heater 102 ismaintained at a temperature of from 700 to 750° C. More particularly,the controller 300 maintains the temperature of the central portion ofthe first heater 102 at 700 to 710° C. based on the temperature datainputted from the first thermocouple 122 and maintains the temperatureof the peripheral portion of the first heater 102 at 740 to 750° C.based on the temperature data inputted from the second thermocouple 123.Here, the central portion of the first heater 102 refers to that portionon which the wafer 200 is positioned. Because the temperature of thecentral portion of the first theater 102 is lower than the temperatureof the peripheral portion of the first heater 102, and the peripheralportion of the first heater 102 is disposed remotely from the wafer 200,the effect that the peripheral portion of the first heater 102 has onheating the wafer is less than the effect that the central portion ofthe first heater 102 has.

[0051] The central portion of the first heater 102 protrudes upwardly bya predetermined distance from the upper surface of the peripheralportion of the first heater 102. As such, a wafer holder 160 (shown inFIG. 2) can be positioned on the periphery of the upper surface of thefirst heater 102.

[0052] As shown in detail in FIG. 4, a silicon layer 210 is formed onthe upper surface of the wafer 200 which is positioned on the firstheater 102. The wafer 200 formed with the silicon layer 210 is fed intothe process chamber 110 by a handler (not shown), and the controlsection 300 operates a valve device 116 (shown in FIG. 2) to open theguide slot 114 so that the wafer 200 can be easily guided into theprocess chamber 110.

[0053] Referring again to FIG. 2, the process chamber 110 includes adome-shaped roof 112. A second heater 105 surrounding the dome-shapedroof 112 is disposed at an upper portion of the dome-shaped roof 112.The radiant heat in the process chamber 110 is efficiently directedtoward the wafer 200 by the dome-shaped roof 112.

[0054] The temperature of the second heater 105 is controlled by thecontroller 300. The controller 300 controls the temperature of thesecond heater 105 to within a range of 300 to 320° C. The controller 300also controls the temperatures of the first and second heaters 102 and105 such that the surface temperature of the wafer 200 is maintainedwithin a range of 625 to 630° C considering also the heat radiatingtoward the wafer in the process chamber 110. For this purpose, thetemperatures of the second heater 105 and the process chamber 110 areinputted to the controller 300 by a sensor device (not shown).

[0055] The apparatus 100 also includes an RF electrode 140 disposedbetween the dome-shaped roof 112 and the second heater 105. When a gassuch as silane, disilane, or the like is injected from the gas injector130, RF electric waves are irradiated into the process chamber 110through the RF electrode 140, thereby activating the gas. The gasinjector 130 is installed at the same level (with respect to thevertical) as the first heater 102 and is connected to a gas supplyingline 138 for receiving the gas from a supply 139 of source gas.

[0056] Furthermore, the apparatus 100 according to the present inventionincludes an insulating member 180 which insulates the interior of theprocess chamber 110 from the environment outside the process chamber 110so that the heat in the process chamber 110 is prevented fromtransferring to the outside of the process chamber 110. The insulatingmember 180 covers the inner wall surface of the bottom portion of theprocess chamber 110. The insulating member 180 is of quartz.

[0057] A space 1 18 is formed in the bottom wall 117 of the processchamber 110. The space 118 is in a vacuum state to prevent heat frombeing transferred from the inner wall surface of the bottom of theprocess chamber 110 to the outer wall surface of the bottom of theprocess chamber 110. According to another form of the present invention,an insulating material such as quartz can occupy the space 118.

[0058] The vacuum within the space 118 reduces the temperature loss inthe process chamber 110 so that the temperature in the process chamber110 is stably maintained, and prevents the outer wall of the processchamber 110 from becoming hot, thereby protecting operating personnel.

[0059] One side of the process chamber 110 communicates with a dischargeport 132. The discharge port 132 is connected to a vacuum pump 135controlled by the controller 300 to allow the process chamber 110 to beevacuated.

[0060] In the process chamber 110, the wafer holder 160 receives thewafer 200 guided toward the first heater 102 in order to place the wafer200 on the upper surface of the first heater 102. The wafer holder 160includes a first arm portion 162 disposed at a peripheral portion of theupper surface of the first heater 102, a second arm portion 164connected to a wafer holder driving apparatus 170, and a support 166which connects the first arm portion 162 to the second arm portion 164.Although only one first arm portion 162, one second arm portion 164, andone support 166 are shown in the figure, the wafer holder comprisesthree or more sets of such components.

[0061] The wafer holder driving apparatus 170 comprises a cylinder 172integral with and disposed at the central portion of the bottom of theprocess chamber 110.

[0062] A plunger 174 is disposed in the cylinder 172 in such a mannerthat it can move upward and downward. An operation rod 176 is engagedwith the upper surface of the plunger 174 and the upper end portion ofthe operation rod 176 is connected to an end of the second arm portion164. A hydraulic pressure supplying section 178 controlled by thecontroller 300 supplies the cylinder 172 with hydraulic pressure tocause the plunger 174 to move upward and downward in the cylinder 172.

[0063] Hereinafter, the operation of the HSG-Si layer forming apparatus100 of the present invention will be described with reference to FIG. 6.

[0064] When the HSG-Si manufacturing process starts, the controller 300causes current to be supplied to the first heater 102 fixed in place inthe process chamber 110 and to the second heater 105 surrounding theupper portion of the process chamber 110 until the temperature in theprocess chamber 110 reaches a constant value (Step S1). Then, thecontroller 300 regulates the temperature of the first heater 102 so asto be within a range of 700 to 750° C. and regulates the temperature ofthe second heater 105 so as to be within a range of 300 to 320° C.

[0065] Thereafter, the valve device 116 is commanded by signals receivedfrom the controller 300 to open the guide slot 114 whereupon the wafer200 is moved into the process chamber 110 by the handler.

[0066] When the wafer 200 is moved to a position over the upper surfaceof the first heater 102, the first arm portion 162 of the wafer holder160 positioned on the peripheral portion of the upper surface of thefirst heater 102 is moved upwardly by the wafer holder driving apparatus170 and thereby receives the wafer 200. The first arm portion 162 isthen moved downward and places the wafer 200 on the central portion ofthe upper surface of the first heater 102 (Step S2).

[0067] The wafer 200 remains there in a stationary state (is fixed onthe first heater 102) for a predetermined time (Step S3). During thistime foreign substances, such as moisture formed on the wafer 200, areremoved by the heat generated by the first and second heaters 102 and105 and the radiant heat in the process chamber 110. At this time, thetemperature of the wafer 200 is maintained within the range of 625 to630° C.

[0068] Thereafter, gas is injected onto the silicon layer of the wafer200 by gas injector 130 to form amorphous silicon (Step S4). The gas isa source gas of the amorphous silicon, such as silane, disilane,trisilane, and dichlorosilane. During this injecting step, the RFelectric waves are irradiated into the process chamber 110 by the RFelectrode 140 to activate the gas. The gas injected onto the wafer 200is thermally decomposed, thereby forming the amorphous silicon layer onthe wafer 200. The amorphous silicon layer is formed on the wafer 200 byrapid thermal chemical vapor deposition or low pressure chemical vapordeposition.

[0069] Thereafter, the wafer 200 is annealed for a predetermined time sothat the amorphous silicon layer formed on the upper portion of thesilicon layer is transformed into an HSG-Si layer (Step S5). The HSG-Silayer 220 is shown in FIG. 5.

[0070] During Steps S1 to S5, the temperature in the process chamber 110and the temperatures of the first and second heaters 102 and 105 aredetected by the sensor device and the first and second thermocouples 122and 123. Also, during Steps S3 to S5, the controller 300 finely controlsthe amount of current supplied to the first and second heaters 102 and105 based on the detected temperatures to thereby maintain thetemperature of the wafer 200 within a range of 625 to 630° C.

[0071] In addition, during Steps S1 to S5, the temperature in theprocess chamber 110 is maintained constant, whereby the temperature ofthe wafer 200 is also maintained constant (from 625 to 630° C).

[0072] When the formation of the HSG-Si layer 220 has been completed,the controller 300 opens the valve device 116 and applies operationsignals to the handler to feed the wafer 200 to the next stage of thesemiconductor fabrication equipment.

[0073] As described above, the HSG-Si layer can be uniformly formed onthe wafer according to the present invention, because the temperature inthe process chamber is maintained constant during the HSG-Simanufacturing process. Furthermore, the HSG-Si layer forming apparatushas a comparatively small number of working parts and hence, acorrespondingly simple structure. Thus, it is economical to manufacture.Still further, the present invention can form the HSG-Si layer in lesstime than the prior art, and thus contributes to the efficiency in themanufacturing process of the semiconductor devices.

[0074] Although the present invention has been described above inconnection with the preferred embodiment thereof, it is to be understoodthat various changes and modifications can be made to the presentinvention within the spirit and scope of the present invention asdefined by the appended claims.

What is claimed is:
 1. Apparatus for forming an HSG-Si layer on a wafer,comprising: a housing constituting a process chamber in which an HSG-Siformation process is performed; a first heater fixed in place in saidprocess chamber so as to be immovable relative to said housing, saidfirst heater having an upper surface on which a wafer is to be supportedwhile an HSG-Si layer is formed thereon; a supply of source gas ofHSG-Si; a gas injector which injects gas into the process chamber, saidgas injector being connected to said supply of source gas and disposedin said process chamber at the same level as said first heater andoriented such that the injector injects source gas into the processchamber toward an upper surface of a wafer supported on said firstheater; and a thermal insulator covering a portion of said housing inwhich said first heater is disposed, thereby suppressing the transfer ofheat in the process chamber to the exterior of the process chamber. 2.Apparatus for forming an HSG-Si layer on a wafer as claimed in claim 1,and further comprising a second heater surrounding an upper portion ofthe process chamber.
 3. Apparatus for forming an HSG-Si layer on a waferas claimed in claim 2, wherein the upper portion of the process chamberis dome-shaped so that heat radiating in said process chamber isdirected by the upper portion of the process chamber toward a wafersupported on the upper surface of said first heater.
 4. Apparatus forforming an HSG-Si layer on a wafer as claimed in claim 2, and furthercomprising a temperature control system which, during the HSG-Si layerforming process, regulates the temperature of the first heater to withina range of 700 to 750° C., the temperature of the second heater towithin a range 300 to 320° C., and thereby regulates the surfacetemperature of a wafer supported on the upper surface of said firstheater to within a range of 625 to 630° C.
 5. Apparatus for forming anHSG-Si layer on a wafer as claimed in claim 4, wherein said temperaturecontrol system comprises a current supply line connected to said heaterat an outer peripheral portion thereof, and a controller which isoperatively connected to said current supply line so as to control thecurrent flowing therethrough to the outer peripheral portion of saidfirst heater such that during the HSG-Si layer forming process, acentral portion of said first heater is maintained at a temperature of700 to 710° C. and the outer peripheral portion of said first heater ismaintained at a temperature of 740 to 750° C.
 6. Apparatus for formingan HSG-Si layer on a wafer as claimed in claim 5, wherein saidtemperature control system further comprises first and secondthermocouples, the first thermocouple being attached to the centralportion of a lower surface of the first heater and extending downwardlytherefrom, and the second thermocouple being attached to the peripheralportion of the lower surface of the first heater at one side thereof andextending downwardly therefrom, such that said thermocouples detect thetemperatures of central and peripheral portions of the first heater,respectively, and said thermocouples being operatively connected to saidcontroller so as to send signals thereto representative of the detectedtemperatures.
 7. Apparatus for forming an HSG-Si layer on a wafer asclaimed in claim 2, and further comprising an RF electrode providedbetween said upper portion of the process chamber and said secondheater, RF electric waves irradiated into the process chamber throughthe RF electrode activating the source gas injected into the processchamber by the gas injector.
 8. Apparatus for forming an HSG-Si layer ona wafer as claimed in claim 1, wherein said housing has a wall formingthe bottom of the process chamber, and said insulator comprises a quartzmember extending over an inner surface of said wall.
 9. Apparatus forforming an HSG-Si layer on a wafer as claimed in claim 8, wherein saidwall has a space extending throughout the interior thereof, and furthercomprising a thermal insulating member occupying said space. 10.Apparatus for forming an HSG-Si layer on a wafer as claimed in claim 1,wherein said wall has a space extending throughout the interior thereof,a vacuum existing in said space whereby the vacuum suppresses thetransfer of heat from an inner bottom wall surface of the processchamber to an outer bottom wall surface of the process chamber. 11.Apparatus for forming an HSG-Si layer on a wafer as claimed in claim 1,and further comprising a wafer holder which receives a wafer transferredinto the process chamber, and a wafer holder driving mechanism whichdrives the wafer holder so as to position the wafer received thereby onthe upper surface of said first heater.
 12. Apparatus for forming anHSG-Si layer on a wafer as claimed in claim 11, wherein the wafer holderdriving mechanism includes a cylinder integral with said housing andextending vertically therefrom at a central portion of the bottom of theprocess chamber, a plunger mounted in said cylinder so as to movableupward and downward, and an operation rod having a first end integralwith an upper portion of the plunger and a second end engaging the waferholder so as to move the wafer holder upward and downward according tothe upward and downward movement of the plunger.
 13. Apparatus forforming an HSG-Si layer on a wafer as claimed in claim 12, wherein saidcylinder is a hydraulic cylinder whereby the plunger is moved upward anddownward according to the pressure of hydraulic fluid in the cylinder,and further comprising a source of hydraulic pressure communicating withsaid cylinder, and a controller operatively connected to said source ofhydraulic pressure so as to regulate the pressure of hydraulic fluidcommunicating with said cylinder.
 14. Apparatus for forming an HSG-Silayer on a wafer as claimed in claim 1, wherein said source gas is oneselected from the group consisting of silane, disilane, trisilane, anddichlorosilane.
 15. A method of forming an HSG-Si layer on a wafer, saidmethod comprising the steps of: providing a process chamber having afirst heater fixed in position at the bottom thereof and a second heaterlocated at the top thereof; placing a wafer onto an upper surface of thefirst heater fixed in said position at the bottom of the processchamber; with the wafer disposed on the upper surface of the firstheater, operating the first and second heaters and exposing the wafer tothe heat generated by the first and second heaters and radiating withinthe process chamber for a period of time sufficient for the heat toremove foreign substances from the wafer; once the period of time haselapsed, injecting a source gas of HSG-Si onto the wafer supported onthe upper surface of the first heater while the heater remains fixed insaid position at the bottom of the process chamber, to thereby from alayer of amorphous silicon on the wafer; with the first heater stillfixed in said position at the bottom of the process chamber, annealingthe wafer for a predetermined period of time so that the amorphoussilicon is transformed into an HSG-Si layer; and regulating thetemperatures of the first and second heaters to maintain the temperatureof the wafer constant from at least once the source gas begins to beinjected into the process chamber through the end of the annealing atthe lapse of said predetermined period of time.
 16. A method of formingan HSG-Si layer on a wafer as claimed in claim 15, wherein the step ofregulating comprises maintaining the temperature of the ambient withinthe process chamber constant from the time the wafer is placed on theupper surface of the heater through the end of the annealing at thelapse of said predetermined period of time.
 17. An HSG-Si manufacturingmethod according to claim 15, wherein the step of regulating comprisesregulating the temperature of the first heater to within a range of 700to 750° C. and the temperature of the second heater to within a range of300 to 320° C., and adjusting the temperatures of the first and secondheaters within said ranges from once the source gas begins to beinjected into the process chamber through the end of the annealing atthe lapse of said predetermined period of time to maintain a surfacetemperature of the wafer within a range of 625 to 630° C.
 18. A methodof forming an HSG-Si layer on a wafer as claimed in claim 15, whereinthe step of injecting source gas toward the wafer comprises injecting agas selected from the group consisting of silane, disilane, trisilane,and dichlorosilane, and further comprising irradiating RF electric wavesinto the process chamber to activate the gas as the gas is beinginjected toward the wafer.
 19. A method of forming an HSG-Si layer on awafer as claimed in claim 15, wherein the step of regulating comprisesdirectly detecting the temperatures of the first and second heaters fromthe time the wafer is placed on the upper surface of the first heaterthrough the end of the annealing at the lapse of said predeterminedperiod of time, and regulating the temperatures of the first and secondheaters based on the detected temperatures to maintain the surfacetemperature of the wafer within a range of 625 to 630° C. from at leastonce the source gas begins to be injected into the process chamberthrough the end of the annealing at the lapse of said predeterminedperiod of time.